The invention relates generally to air conditioning and refrigeration systems, and more specifically to a method of controlling the operation of a refrigeration system with temperature sensors located in the return air port and discharge air port.
Refrigeration systems control the temperature of a load space to stay within a desired temperature range surrounding a set point temperature. The load space air temperature is measured by a sensor disposed in either the path of air returning to the refrigeration system from the load space (return air), or in the path of air discharged from the refrigeration system to the load space (discharge air). Some uses of refrigeration systems have a preference for return air control and some have a preference for discharge air control. As disclosed in U.S. Pat. Nos. 3,973,618 and 4,977,752, both assigned to the same assignee as the present application, both a return air sensor and a discharge air sensor may be provided.
Many factors influence the load space air temperature. Warm or cool ambient air may enter the load space and affect the load space air temperature when the load space door is ajar. Additionally, when the refrigeration system is used in connection with a transportable load space, e.g. a truck trailer, the warmth of the sun hitting the exterior of the load space, a cool rain or snow hitting or accumulating on top of the load space, or even a change in altitude as the load travels from point to point can influence the load space air temperature. Therefore, the temperature of the conditioned air required to maintain the load space air temperature in the desired set point range changes as the load space air temperature is influenced by these factors. In some instances it becomes necessary to switch between return air control and discharge air control to maintain the load space air temperature within the desired set point range.
Currently available refrigeration systems require manual switching between return air control and discharge air control. In these applications, an operator must monitor the operating conditions of the air-conditioned space and the refrigeration system and then must switch between return air control and discharge air control based upon these conditions.
The present inventive method of operating a refrigeration system is designed to condition a conditioned space to a set point temperature. The refrigeration system includes a discharge port that guides conditioned air from the system to the conditioned space and a return port that guides air from the conditioned space back to the system. The method comprises providing a first control algorithm and second control algorithm for controlling the system. The first control algorithm is a function of the air temperature at the discharge port, and the second control algorithm is a function of the air temperature at the return port. The method further comprises operating the system using the first control algorithm when a first condition is met, operating the system using the second control algorithm when a second condition is met, and automatically switching between the first control algorithm and the second control algorithm depending on the status of the first condition and the second condition.
In preferred embodiments, the method further comprises measuring the temperature of ambient air outside of the conditioned space, comparing the ambient air temperature to the set point, controlling the system utilizing the first control algorithm if the ambient air temperature is greater than or equal to the set point, and controlling the system utilizing the second control algorithm if the ambient air temperature is less than the set point.
Operating the system using the second control algorithm when the second condition is met includes operating the system in the high speed heat mode if the return air temperature is more than about 5 degrees below the set point and operating the system in the low speed heat modulation mode if the return air temperature is less than about 1.5 degrees above the set point.
The system can also operate in the first control algorithm in a low speed cool modulation mode and a low speed cool mode. Operating the system using the first control algorithm when the first condition is met includes operating the system in low speed cool mode if the return air temperature is less than about 0.5 degrees below the set point and operating the system in low speed cool modulation mode if the return air temperature is less than about 3 degrees above than the set point.
Additional features and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description, claims, and drawings.